In general, the function of a laminating adhesive is to join together very fine films of different or similar substrates, e.g., polyethylene, polypropylene, polyester, polyamides, metal, paper or cellophane to form composite films used for many different purposes. A suitable laminating adhesive is expected to provide excellent bonds on numerous substrates with only a small application of adhesives.
Acrylic emulsions or dispersions are also used in commercial applications as adhesives or coatings and have been described in U.S. Pat. Nos. 4,558,092, 4,403,003, 4,322,328, 4,609,690, 4,522,973 and 4,525,510.
Guagliardo, U.S. Pat. No. 4,318,833 is directed to a coating composition comprising an ethylenically unsaturated monomer polymerized insitu in the presence of a water soluble polyurethane. Guagliardo does not employ acid, amine or hydroxy functional monomers in the acrylic monomer since it would react with or terminate the isocyanate prepolymer.
Aqueous linear or crosslinked aqueous polyurethane dispersions may be used in a wide range of commercial applications such as coatings and adhesives as shown in several patents including U.S. Pat. Nos. 5,147,926, 5,610,232, 5,637,639, 5,608,000 and 5,334,690.
Meichsner et al., U.S. Pat. No. 5,147,926 disclose crosslinkable aqueous polyurethane dispersion having long shelf life and containing polyurethanes which have carbonyl and polyhydrazides and their use for the preparation of printing inks.
Yasuhiro et al., U.S. Pat. No. 5,01,881 is directed to aqueous coating composition comprising aqueous acrylic resin and urethane resin emulsion in the absence of a crosslinking agent. The coatings are used for plastic substrates.
Mitsuji et al., U.S. Pat. No. 5,281,655 is directed to aqueous coating composition for metallic and plastic substrates. The composition comprising a urethane resin emulsion, a resin for use in aqueous coating composition and a hydrophobic melamine resin as a crosslinking agent. There is no disclosure regarding the use of the composition as a laminating adhesive.
Loewrigkeit et al., U.S. Pat. No. 4,644,030 discloses a process wherein isocyanate-terminated polyurethane dispersions are polymerized using a free radical initiator.
There remains a need for a water based laminating adhesive composition that exhibits excellent adhesion in a variety of film/film and film/foil, etc. lamination applications. The laminating adhesive composition overcomes the drawbacks of the prior art. Surprisingly, the laminating adhesive composition of the present invention provides improved adhesion, bond strength and resistance properties, as well as excellent processability and storage stability as compared to other laminating adhesive compositions.